1. Technical Field
Exemplary aspects of the present invention generally relate to a frame structure for use in an image forming apparatus and an image forming apparatus including the frame structure.
2. Related Art
Related-art image forming apparatuses, such as copiers, printers, facsimile machines, and multifunction devices having two or more of copying, printing, and facsimile capabilities, typically form a toner image on a recording medium (e.g., a sheet of paper, etc.) according to image data using, for example, an electrophotographic method. In the electrophotographic method, for example, a charger charges a surface of a latent image carrier (e.g., a photoconductor); a writing device emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a developing device develops the electrostatic latent image with a developer (e.g., toner) to form a toner image on the photoconductor; a transfer device transfers the toner image formed on the photoconductor onto a sheet of recording media; and a fixing device applies heat and pressure to the sheet bearing the toner image to fix the toner image onto the sheet. The sheet bearing the fixed toner image is then discharged from the image forming apparatus.
A tandem-type full-color image forming apparatus includes multiple photoconductors. Light beams are directed from the writing device onto the photoconductors to form latent images on the respective photoconductors. The latent images are developed with toner of different colors so that toner images of the different colors are formed on the respective photoconductors. The toner images thus formed on the photoconductors are then sequentially transferred one atop the other onto a transfer body included in the transfer device to form a single full-color toner image on the transfer body.
In such a configuration, if formed at different positions on the respective photoconductors offset from one another, the latent images are also transferred offset from one another onto the transfer body, causing a so-called color shift in the resultant full-color image. One cause of such offset is unequal distances between the writing device and the respective photoconductors. To accurately position the photoconductors and the writing device relative to one another within the image forming apparatus, front and rear plates, each of which positions the photoconductors, and a writing device frame that positions the writing device need to be accurately fixed in place in the main frame of the image forming apparatus.
There is known a frame structure for use in an image forming apparatus in which first a writing device frame is mounted to the main frame, and then front and rear plates are mounted to the writing device frame. FIG. 1 is a perspective view of a main frame 201 of a related-art image forming apparatus. Multiple stays 201a, 201b, 201c, 201d, 201e, 201f, 201g, 201h, 201i, 201j. 201k, and 201l are assembled together into the main frame 201.
FIG. 2 is a perspective view of the main frame 201 illustrated in FIG. 1, to which a writing device frame 202 is mounted. The rectangular writing device frame 202 is placed on and fixed to the horizontal stays 201c and 201d of the main frame 201 with screws, so that the writing device is supported by and fixed to the writing device frame 202. Each of a front frame member 202D and a rear frame member 202C of the writing device frame 202 has positioning pins 203 at two separate positions (the positioning pins 203 for the rear frame member 202C are not shown in FIG. 2).
FIG. 3 is a perspective view of the main frame 201 illustrated in FIG. 1, in which front and rear plates 204 and 205 are mounted to the writing device frame 202. The front plate 204 is fitted with the positioning pins 203 of the front frame member 202D to be positioned relative to the writing device frame 202. Then, the front plate 204 is fixed to the writing device frame 202. In a manner similar to the front plate 204, the rear plate 205 is fitted with the positioning pins 203 (not shown) of the rear frame member 202C to be positioned relative to the writing device frame 202. Thereafter, the rear plate 205 is fixed to the writing device frame 202. Each of the front and rear plates 204 and 205 has positioning holes 206 that position photoconductors. The photoconductors, not shown, are fitted with the positioning holes 206 formed in both the front and rear plates 204 and 205, respectively, to be positioned within the image forming apparatus.
In the above-described configuration, the front and rear plates 204 and 205, each of which positions the photoconductors, are directly fixed to the writing device frame 202 that positions the writing device. However, unlike the above-described configuration, in a case in which the front plate 204, the rear plate 205, and the writing device frame 202 are fixed to the main frame 201 individually, tolerances of the main frame 201 accumulate between the rear plate 205 and the writing device frame 202 and between the front plate 204 and the writing device frame 202, respectively. Consequently, the writing device frame 202 and the front plate 204 or the rear plate 205 are not accurately positioned relative to each other.
By contrast, in the above-described configuration, the front plate 204 and the rear plate 205 are directly fixed to the writing device frame 202. As a result, accumulation of tolerances of the main frame 201 is eliminated, thereby achieving accurate relative positioning of the writing device frame 202 and each of the front and rear plates 204 and 205, respectively. Thus, inequality of the distance between the writing device and each photoconductor is prevented, thereby preventing color shift in resultant images. However, because the main frame 201 is constructed of the multiple stays 201a to 201l assembled together, a force exerted on the main frame 201 in a direction perpendicular to the rear plate 205, that is, a direction indicated by arrow F in FIG. 3, may bend the front stays 201e and 201f and the rear stays 201g and 201h, each of which is designed to extend in the vertical direction, resulting in deformation of the main frame 201.
To prevent deformation of the main frame 201, it is conceivable to increase the number of stays assembled together into the main frame 201 and thus improve the strength of the main frame 201. However, the increase in the number of stays also increases production costs and the weight of the frame structure.